1. Field of the Invention
The present invention relates to a smoke- and water-vapor-permeable food casing based on aliphatic polyamide and/or aliphatic copolyamide.
2. Description of Related Art
In the industrial and craft production of cold-, warm- or hot-smoked raw sausages, scalded-emulsion sausages and cooked-meat sausages, and also processed and fresh cheeses, cellulose casings, cellulose fiber casings and collagen casings and also single-layer or multilayer, water-vapor-permeable plastic casings based on polyamide and in combination with other plastics have proved useful.
In particular in the case of raw sausages, the use of water-vapor-permeable casings is indicated in order to make possible a drying process during ripening to decrease the content of free water in the sausage mix. The water loss can be 0.5% to 50%, based on the starting weight of the sausage. In Salami ripening, for example a weight loss of about 23 to 26% after 10 ripening days is customary, which assumes high-permeability casings. Furthermore, customary plastic casings do not allow cold smoke through (this has a temperature of about 20 to 35° C.) and only small amounts of hot smoke (approximately 70 to 80° C.). However, cold smoking with raw sausage varieties is a standard method. The smoking process, depending on the method, can take from 20 min to several days.
During the smoking, either the smoke generated within a closed chamber (smoking chamber), or the smoke introduced into this chamber is brought to the suspended sausage, or circulated over the goods to be smoked. Alternatively to this, a liquid smoke solution can be nebulized within the chamber.
To achieve a uniformly good smoking result, the sausages must be suspended so that they are accessible to the smoke from all sides. To achieve a uniform smoked color and smoked aroma, the sausages must not touch and also cannot be smoked lying down. It is typical in this case that sausages or sausage links are brought into the smoking chambers in mobile racks hanging on smoke skewers. The sausage hangs here on its own holding loop mounted in the closure clip.
Suspension on the smoke skewers is performed manually or mechanically. The smoke skewers themselves can only be hung up manually in the smoke carts. After the smoking process, the sausage is cleaned from adhering soot particles and dried. Owing to a high drying shrinkage, however, oil can escape at the clip, so that the sausage is coated with a fat film. This has long been considered as a disadvantage and hygiene risk by the meat-processing industry.
After the drying phase, the smoke skewers are taken out of the smoke cart and the sausage is taken off from the smoke skewers. The sausage links are cut into individual sausages and then packed, the suspension loops having to be removed before packaging.
Smoking is generally very labor-intensive and increases the production costs. The operation of smoking chambers is subject to supervision by law with the focus on emission protection and fire precautions. Smoking chambers and the tools used for smoking (smoke carts and smoke skewers) must be regularly cleaned using chemical cleaning agents, with high labor requirements and high personal use, and maintained. Alternatives to simplify the smoking process with the elimination of smoking chambers are still being sought.
To transfer smoke flavor and aroma to sausage products, in addition to the methods of traditional smoking and smoking using liquid smoke, there is the possibility of directly impregnating sausage casings with liquid smoke. In the prior art, smoke- and water-vapor-permeable polymer casings are alternatively described which are smokeable, or smoke- and water-vapor-impermeable polymer casings which can be impregnated with liquid smoke.
Casings for unsmoked sausage products are currently produced to a great extent from thermoplastics. Conventional plastics are polyamides, polyesters and vinyl chloride copolymers. The casings can be produced as a single layer or multilayered. In the multilayered casings, frequently, layers of polyolefin are also present. The critical advantage of these casings is the technically relatively simple and inexpensive production. Casings made of thermoplastic generally have water vapor transmission rate (WVTR) of about 3 to 20 g/m2 d. Sausage products in such a casing loose markedly less weight during storage. Such casings, for instance made of polyamide, are generally not smoke-permeable, and can therefore not be used for producing sausage varieties which are smoked.
It is further known to coat or impregnate tubular food casings, especially sausage casings, on the outside or inside with liquid smoke. Coatings on the outside are simpler to carry out technically. The constituents of the liquid smoke must then migrate through the casing, however, in order to give the emulsion the typical color, aroma and flavor of smoked goods. Cellulose casings impregnated from the outside with liquid smoke are frequently described. Casings made of a different material are frequently not permeable enough for this. This applies for single-layer plastic casings, but very particularly for multilayered plastic casings. These can at any rate be treated with liquid smoke on the inside, which, however, regularly fails because the liquid smoke does not adhere sufficiently and collects to form drops before it is dried. An approach to a solution of this problem is described in DE-A 196 08 001. It consists of applying the liquid smoke to an appropriately cut to size flat film which is then formed into a tube in such a manner that the side coated with liquid smoke faces inward. The tube is then permanently sealed by hot sealing, as a result of which it acquires a longitudinal seam. The liquid smoke is applied, and the tube produced, virtually directly before stuffing with sausage emulsion. Thus shirring the sealed tube is unnecessary. The method, however, requires technically complex, and correspondingly expensive, apparatuses.
WO 97/36798 describes a hot-shrinking planar or tubular food casing which contains on the interior a layer of a copolymer and a food additive. The copolymer contains substantially water-insoluble and hygroscopic segments. As food additive, liquid smoke is also disclosed which is transferred from the casing to its contents. However, it has proved to be a problem that the interior sides stick to one another. This is particularly the case when the casing is stored for a relatively long time in rolled-up or shirred stick form.
A very similar shrink film is also disclosed in WO 98/31731. Here, the interior coating consists of a mixture having (i) an additive which is a flavorant, an odorant, a colorant, an antimicrobial agent, a chelating agent and/or an odor-absorbent, (ii) a polysaccharide or protein as binder and (iii) a crosslinker which has at least two carbonyl groups. The additive can be, inter alia, liquid smoke. Tubular films coated on the interior are produced in this case from the corresponding flat films. The coating itself is performed using a roller. In this case the edges are not coated. The flat film is then formed into a tube and the edges of the film which are laid one above the other are firmly bonded by hot sealing. The resultant casing is shirred and closed at one end with a clip. The casing is then stuffed with a meat product and heated. The additive present in the interior layer of the casing is transferred in the course of this to the meat product. However, the interior sides of the casing frequently stick to one another after shirring, so that on deshirring the interior layer is damaged.
JP-A 139401/2000 describes a film by which a food coloring may be applied to sausage emulsion, ham or similar foods. This is achieved using a coating which, in addition to the food dye, also contains an edible plasticizer such as glycerol, sorbitol or propylene glycol.
EP-A 139 888 discloses a method for smoking foods in a casing made of aliphatic polyamide. The polyamide takes up at least 3% by weight, preferably at least 5% by weight, of water. Smoking is therefore performed in the presence of water or water vapor which requires a climatically controlled smoke chamber.
DE-A 198 46 305 relates to a barrier casing made of a plastic material which has on the inside a layer made of a sorbent material (woven fabric, knits), which is impregnated with colorants or flavorants. During boiling or scalding, the colorants or flavorants are transferred to the casing-enclosed food. The internal layer of the casing is generally bonded to the adjacent layer of the casing by a glue. The barrier casing itself consists, for example, of polyamide and polyethylene layers. Tubular casings are generally produced from corresponding flat films by hot-sealing or gluing. In the region of the sealing seam, the colorant or flavorant is frequently transferred nonuniformly. Sealed or glued casings frequently also display an uneven shrinkage. Then, after scalding or boiling of the sausage, in the seam regions, an unwanted jelly deposit is found between casing and sausage emulsion.
A multilayer plastic casing impregnated on the inside with a mixture of liquid smoke and a browning agent is described in DE-A 101 24 581. It comprises one aliphatic polyamide-based layer in each case on the interior and exterior, and also a central water-vapor-barrier, if appropriate, also oxygen-barrier, layer. This middle barrier layer consists, for example, of polyethylene or ethylene/vinyl alcohol copolymer. The liquid smoke mixture is to act for at least 5 days on the interior before the casing is soaked and stuffed.
All known casings having an interior layer or interior coating which contains a transferrable food additive have the disadvantage that the adhesion of the layer cannot be set in any desired manner. The consequence of insufficient adhesion is that the sausage has a tendency to gel formation and that the coating, on final processing (in the case of tubular films customarily by shirring and/or inverting) displays cracks or even bursts. The casing is then no longer usable. In the event of excessive adhesion, colorants, flavorants or odorants do not transfer to the food to a sufficient extent.
A smokeable film for packaging foods is described in EP-A 217 069. It comprises at least one layer which consists of a mixture of polyamide, an ethylene/vinyl alcohol copolymer (EVOH) and polyolefin, the constituents of the layer being in a defined weight ratio. The layer has a water vapor permeability of less than 40 g/m2·d at a temperature of 40° C. and a relative humidity of 90%. Under customary conditions, satisfactory smoke passage is thus not to be expected.
A water-vapor- and smoke-permeable food casing based on polyamide is also disclosed in WO 02/078455. The casing consists of a matrix of aliphatic polyamide or aliphatic copolyamide and a disperse phase of a low- or high-molecular weight hydrophilic component, such as polyvinylpyrrolidone, polyacrylamide.